1. Field of the Invention
The invention relates to a driving unit for pressure application shaft to be driven by a motor in a welding apparatus, wherein a ball screw mechanism for converting rotation of an output shaft of the motor into a reciprocating motion of the pressure application shaft is housed in a housing and a direct acting type rolling guide mechanism is provided between the pressure application shaft for holding the ball screw mechanism and the housing.
2. Related Art
A driving unit for pressure application shaft in a welding gun connected to a wrist of a robot has been conventionally disclosed in, for example, Japanese Patent Laid-Open Publication No. 9-47881, wherein a ball screw mechanism for converting rotation of an output shaft of the motor into a reciprocating motion of the pressure application shaft is housed in a housing and a direct acting type rolling guide mechanism is provided between a pressure application shaft member and the housing.
In this known driving unit for pressure application shaft, the pressure application shaft for holding the ball screw mechanism is arranged inside a cylinder constituting the housing, a ball box constituting the direct acting type rolling bearing is fixed to the rear end of the pressure application shaft, and a rail provided with a guide groove at the face confronting the ball box is fixed to the inner wall of the cylinder, whereby these components are assembled inside the cylinder, thereby completing the driving unit for pressure application shaft.
However, in the prior art, since the driving unit for pressure application shaft comprising the rail, the bearing, the ball screw mechanism, and so forth are assembled in the housing, an assembling process thereof is troublesome. Hence, it is difficult to manufacture a product having high accuracy, which results in high manufacturing costs.
The invention has been developed to solve the foregoing problem of the prior art, and has an object to provide a driving unit for pressure application shaft in a welding apparatus having components constituting the driving unit for pressure application shaft which are integrally assembled with one another, wherein the driving unit for pressure application shaft is integrally fixed to a housing body. A driving unit for pressure application shaft having a high accuracy is therefore achieved at a low cost.
To achieve the above object, the driving unit for pressure application shaft in a welding apparatus driven by a motor according to the invention includes a housing 8 for housing therein a ball screw mechanism 11 for converting rotation of an output shaft of a motor 1 into reciprocating motion of a pressure application shaft 7, and a direct acting type rolling guide mechanism 12, 13 provided between a pressure application shaft member and the housing 8. The housing 8 comprises a housing body 9 which is opened at one side and has a substantially U-shape in cross section, and a plate 10 for covering the opened portion, and wherein pressure application mechanism members comprise the ball screw mechanism 11, the pressure application shaft member, the direct acting type rolling bearing 12 which is fixed to the pressure application shaft member, and a rail 13 combined with the direct acting type rolling bearing 12, and wherein the pressure application mechanism members are fixed to the housing body 9, and the plate 10 is fixed to the opened portion of the housing body 9.
Further, the driving unit for pressure application shaft in a welding apparatus is characterized in that a front end of the housing 8 is covered with a front wall 21, and a penetration hole 22 through which the pressure application shaft 7 is inserted is formed on the front wall 21, and no bearing is provided in the penetration hole 22.
Further, the driving unit for pressure application shaft in a welding apparatus is characterized in that a rear end of a fixed arm is fixed to the U-shaped housing body 9.
Further, the driving unit for pressure application shaft in a welding apparatus is characterized in that the U-shaped housing body 9 is formed by an extrusion molded member made of aluminum alloy.
Further, the driving unit for pressure application shaft in a welding apparatus is characterized in that a machining portion for manually rotating a ball screw shaft is formed at the rear end of the ball screw shaft of the ball screw mechanism 11.